1. Field of the Invention
The present invention relates generally to well apparatus. In particular, it pertains to apparatus for artificially lifting fluids through a well conduit. Still more specifically, the invention concerns a receiver for connection in a well conduit and a corresponding tool for installation in the receiver to control injection of gas into a column of liquid.
2. Brief Description of the Prior Art
Petroleum wells normally employ a tubing string extending from the surface of the well into a producing formation. The tubing string is usually concentrically surrounded by a larger diameter casing string. In many wells, the producing formation is under sufficient pressure to force the petroleum liquids up the tubing string. However, the producing formation of many other wells may lack the natural pressure necessary for natural flow of liquids to the surface. In such cases, an artificial form of lift must be employed. One popular method of artificial lift is "gas lifting". In gas lifting, a relatively high pressure gas is injected into the liquid to be produced, in order to aerate or lighten the fluid column to produce a mixture of lower specific gravity and induce flow of the mixture to the surface. Some gas lift systems are continuous while others are intermittent.
In contrast to petroleum producing formations, water-bearing formations are almost always without sufficient pressure for a natural flow production. Therefore, some form of artificial lift must be provided. Most water wells of the past have usually been provided with a mechanical pump of some type to lift the water to the surface. However, gas lift systems may also be utilized in providing artificial lift for water wells.
In gas lift systems, wheter used on petroleum or water wells, a tubing string is usually concentrically surrounded by a larger diameter casing string. Gas lift valves may be attached at one or more levels along the tubing string for controlling injection of gas into the fluid column to be lifted. In many wells, the gas is injected through the casing string into the tubing string through which the fluid being produced flows. However, the opposite is true in many cases, i.e. gas is injected through the tubing string into the surrounding fluid column within the casing string. Such a method may be resorted to when it is desirable to move very large volumes of fluids.
In the past, whether fluid production is through the tubing or casing string, gas lift valves have been attached to the tubing string as it is run into the well. Such installations require pulling the tubing string in order to replace or repair a malfunctioning valve. More recently, receivers have been provided for connection in the tubing string so as to allow installation or removal of the gas lift valves through the tubing string without having to pull the tubing string itself. In such cases, the gas lift valves may be run on a wire line or pumpdown tool to a corresponding receiver where it is latched into place. The valve is sealingly placed into communication with some kind of port through which gas is injected into the desired column, whether it is the tubing string or casing string.
The tubing string is limited in flow area and with the installation of gas valves therein is even further limited. This creates somewhat of a problem where relatively high volumes of flow are desired. This is particularly true in cases where gas is injected from the tubing string into the casing string for high volume fluid production. Such is the case in water wells which are produced for high volume water flood operations. Such high volume requirements are more frequent in today's global search for petroleum.
Another problem encountered in high rates of injection and flow is erosion. With normal gas lift operations the ports through which the gas is injected normally open directly toward the wall of the surrounding pipe string. With the extreme flows required in high volume production, the gas may erode and eventually cut through the casing wall, necessitating a complex and extremely costly remedial operation. In fact, it may even result in abandonment of such a well. Another problem encountered in extreme flows is thermal expansion due to the increased temperatures resulting from such high flows. Conventional gas lift installations of the past do not suitably provide for such thermal expansion.